1. Field of the Invention:
The invention relates in general to magnetic cores for electrical inductive apparatus, such as distribution transformers, and more specifically to a new and improved support fixture for defining the window of a magnetic core constructed of amorphous metal alloy.
2. Description of the Prior Art:
Amorphous metal alloys, such as Allied Metglas Product's 2605SC and 2605S-2, exhibit a relatively low no-load loss when used in the magnetic core of an electrical transformer. Co-pending application Ser. No. 896781, now U.S. Pat. No. 4,709,471, filed Aug. 15, 1986, entitled "Method of Making a Magnetic Core", which is assigned to the same assignee as the present application, discloses new and improved methods of constructing magnetic cores of such amorphous material. The new and improved methods include utilizing the extreme flexibility of an amorphous core, normally considered a manufacturing problem, to aid in providing an openable joint in the core. The amorphous magnetic core, which is wound in a round configuration in a preferred embodiment of the co-pending application, is cut to provide a plurality of cut lamination turns, and the cut lamination turns are assembled about a substantially rectangularly shaped fixture. A joint is formed in the assembled lamination turns to form a closed loop, and the rectangularly shaped core loop is subjected to a stress-relief anneal heat treatment cycle to remove winding induced and shaping stresses from the cut lamination turns. After the heat treatment cycle, the core joint is opened and the fixture which defines the core window is disassembled to the point where pre-formed electrical coil assemblies, which include high and low voltage windings, may be slipped over leg portions of the magnetic core loop. The window fixture is then reassembled, and the core joint rebuilt about the fixture. The fixture remains in the assembled core-coil assembly. The hereinbefore mentioned co-pending application is hereby incorporated into the specification of the present application by reference.
It is of critical importance that the periphery of the window fixture be the same as the periphery of the winding mandrel upon which the core loop was originally wound, within a predetermined small tolerance. This critical dimension must be held and maintained each time the fixture is assembled, notwithstanding the fact that the fixture has been subjected to a heat treatment cycle along with the amorphous alloy. The fixture must be rigid and have a high mechanical strength, to enable the core loop to be formed about about the fixture with a good space factor, in effect using the fixture as a forming tool. The fixture must provide precise control over the corner dimensions of the substantially rectangularly shaped core loop, while being quickly and easily assembled and disassembled. The fixture must be easily and quickly manufacturable to different dimensions using the same tooling, in order to economically accommodate different sizes of magnetic cores for use in transformers of different power ratings. Finally, since the fixture is not reused, but is an integral part of a completed transformer, it must provide all of the above characteristics while being manufacturable at a very low cost.